Motorcycles with centrifugal clutches are conventionally known. For example, U.S. Pat. No. 6,533,056 B1 to Maimone discloses a motorcycle which includes a centrifugal clutch. The centrifugal clutch is automatically engaged during motorcycle starting and automatically disengaged during stopping. Thus, there is no need for a rider to operate the clutch during motorcycle starting and stopping. The rider only operates the accelerator at starting and stopping with the burden on the rider as far as operation of the clutch is concerned being mitigated.
However, in a conventional motorcycle with a centrifugal clutch, such as the one described by Maimone, the centrifugal clutch is constantly disengaged while the motorcycle is in an idling state, and the vehicle cannot, therefore, slow down via engine breaking. Due to this, even at slow driving or the like during traffic jam, the vehicle cannot run unless the rider operates the accelerator to raise the rpm (revolutions per minute) of the engine to be equal to or larger than a predetermined number of revolutions. However, during a traffic jam or the like, even if a throttle is opened to raise the engine rpm to achieve temporary acceleration, the vehicle cannot continue to run at the accelerated speed and the vehicle is subsequently often forced to come to a stop by braking operation or the like. Therefore, it is often disadvantageously necessary to frequently open/close the vehicle throttle.